Impedance transformer



March 19, 1946. L M. LET-:Ds 2,396,708

IMPEDANCE TRANSFORMER Filed Sept. 14. 1942 Fig. I. ff A/4/ v I i 3 f 6Fig. 2.

Inventor:

Laur'ance M. Leeds,

b 8 His Attorneg.

Patented Mar. 19, 1946 UNITED'ISTATES PATENT OFFICE IMPEDANCETRANSFORMER Laurance M. Leeds, Rotterdam Junction, N. Y.,

assignor to General Electric Company, a corporation of New YorkApplicationseptember 14, 1942, Serial No. 458,306 2 Claims. (Cl. 178-44)The present invention relates to an arrangement for improving theoperation of a quarter wavelength transmission line used as an impedancematching transformer under conditions where there is unavoidable seriesor shunt reactance. The unavoidable reactance has the eifect ofintroducing an apparent reactance which has heretofore been compensatedby changing the length of the transmission line with a resultantreduction in the transformer ratio.

The object of my invention is to 'provide an arrangement in which theeffect of unavoidable -reactance is eliminated without changing the vseries with a resistance 8 at the output. If the reactances X2 and X1are related by the equation Zo =X2X1 I (1) where Z is the characteristicimpedance of the transmission line, the transformer ratio between theinput terminals 4 and the terminals '5 of the resistance. 3 is givenbythe equation where Z1- is the terminating resistance 3 and Z. is theapparent value of this resistance measured at the input terminals 4.-This equation is identical with that which would be obtained if thereactances X2 and X1 were eliminated. The reactances X1, X2 accordinglyprovide perfect compensation without changing the impedance transformerratio.

r The relations set forth above can be proved by considering theimpedance at the input terminals 4 as equal-tothe reactance-Xa inparallel with from which it is apparent that the impedance ratio will begiven by the equation- It will be noted that the reactances X1 and X:may be either inductances or capacitors and that either may be theunavoidable reactance. In the most'common case, the reactance & will bedistributed capacity which will be compensated by a capacity X1 inseries with the terminating resistance. p

In Fig. 2 the reactance X1'is in parallel with theterminating'resis'tance 3 and the reactance X2 is in series with theterminals 4 of the quarter wavelength transmission line I. The impedanceconnected across theterminals 5 consists of the terminating resistanceZr in parallel with the reactance X1 and is equal to ril r+j l where Ximay be eitherpositive (inductance) or negative (capacity).

The apparent'value at the terminals 4 or the impedance orthetransformer, is equal to the the rest of the. circuit. Theinputimpedance Z; A

will be given by the equation or negative (capacity) The equationreduces to the form sum of the reactance X2 and the impedance at theterminals 4 is given by the equations As in Fig. 1, either of thereactances X1, X: may be lnductances or capacities and the effect of oneis compensated by the other.

What I claim as new and desire to secure by Letters Patentot the'UnitedStates is:

transmission line and X is the reactance or the i0 unavoidable shuntcapacity.

2. An impedance matching transformer comprising a quarter wavelengthtransmission line having a series reactance'at one end and a shuntreactanceat the other end, the reactances having values determined bythe equation Zn'=X1Xzwhere Z0 is thecharacteristic impedance of thetransmission line and X1 and x: are the respective reactances.

LAURANCE M. IEEDS.

